Smells like nostalgia: Why do scents bring back memories?

The smell of chlorine wafts through the air. Suddenly, you recall childhood summers spent in a swimming pool. Or maybe it's a whiff of apple pie, or the scent of the same perfume your mom used to wear. Our noses have a way of sniffing out nostalgia.

“I stepped into an elevator and a bunch of people piled in behind me. I was behind a woman with her back to me, her hair was in my nose, and I could smell the perfume, Shalimar, and I hadn’t smelled it in [years]. It seemed like I was transported back to high school,” says Howard Eichenbaum, director of the Laboratory of Cognitive Neurobiology at Boston University.

While all the senses are connected with memories, smell in particular sparks a flurry of emotional memories. Why?

After a smell enters the nose, it travels through the cranial nerve through the olfactory bulb, which helps the brain process smells. The olfactory bulb is part of the limbic system, the emotional center of the brain. As a member of the limbic system, the olfactory bulb can easily access the amygdala, which plays a role in emotional memories (it’s also where the "fight or flight" reflex comes from).

“Olfactory has a strong input into the amygdala, which process emotions. The kind of memories that it evokes are good and they are more powerful,” explains Eichenbaum.

This close relationship between the olfactory and the amygdala is one of the reason odors cause a spark of nostalgia.

“We don’t use emotional memory that much,” says Dr. Ron DeVere, director of the Taste and Smell Disorders Clinic and the Alzheimer’s Disease and Memory Disorders Center, in Austin, Texas, and member of the American Academy of Neurology (AAN). He adds that when people consciously attempt to remember something they focus on the details, not feelings.

“You have an odor, you may not identify the odor, but you are associating that with some memories. The first time you smelled apple pie you may have been at your grandmother’s house,” DeVere says.

Also at play is a relationship between the olfactory system and the hippocampus, which is critical to developing memories. Even though the olfactory system interacts with the emotion and memory centers in the brain, it does not connect with more developed regions.

“Smells do bring back memories,” says Dr. Ken Heilman, James E. Rooks Jr. Distinguished Professor Neurology and Health Psychology at the University of Florida and a member of AAN. “Smell goes into the emotional parts of the brain and the memory parts, whereas words go into thinking parts of the brain.”

This could explain why memories sparked by smell feel nostalgic and emotional, rather than concrete and detailed. Also, Eichenbaum notes that primates evolved to rely mostly on vision, not smell, so these memories are less reliable. (If you were a rat in his lab, your smell memories would be more detailed).